The present invention generally provides apomictic soybean varieties and more particularly, apomictic soybean varieties having a determinate growth habit, a percent conversion greater than 60% for conversion of flowers to pods and at least 100 pods per plant. The present invention further provides methods for producing apomictic soybean varieties comprising selecting double-ovule seeds, growing said seeds and then selecting for apomictic varieties.
There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of desired goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the desired goals. The goal is to combine in a single variety an improved combination of desirable traits from the parental germplasm. These important traits may include higher seed yield, resistance to diseases and insects, better stems and roots, tolerance to drought and heat, better agronomic quality, resistance to herbicides, and improvements in compositional traits.
Reproduction in plants is ordinarily classified as sexual or asexual. The term apomixis is generally accepted as the replacement of sexual reproduction by various forms of asexual reproduction. Apomixis is a genetically controlled method of reproduction in plants where the embryo is formed without union of an egg and sperm nuclei. There are three basic types of apomictic reproduction: 1) apospory—embryo develops from a chromosomally unreduced egg in an embryo sac derived from the nucellus, 2) diplospory—embryo develops from an egg in an embryo sac derived from the unreduced megaspore mother cell, and 3) adventitious embryony—embryo develops directly from a somatic cell. In most forms of apomixis, pseudogamy or fertilization of the polar nuclei to produce endosperm is necessary for seed viability. Obligate apomicts are believed to have a completely closed recombination system; that is, recombination occurs only during microsporogenesis and is absent during megasporogenesis. In facultative apomicts, both apomictic and sexual modes of reproduction coexist.
The aforementioned types of apomixis have economic potential because they can cause any genotype, regardless of how heterozygous, to breed true. It is a reproductive process that bypasses female meiosis and syngamy to produce embryos genetically identical to the maternal parent. With apomictic reproduction, progeny of specially adaptive or hybrid genotypes would maintain their genetic fidelity throughout repeated life cycles. In addition to fixing hybrid vigor, apomixis can make possible commercial hybrid production in crops where efficient male sterility or fertility restoration systems for producing hybrids are not known or developed. In addition, apomixis can increase the reproductive capacity of plants with distorted or adverse chromosome constitutions.
Apomixis can make hybrid development more efficient by eliminating the need for multiple crosses. It also simplifies hybrid production and increases genetic diversity in plant species with good male sterility systems. It would be ideal to find genes controlling obligate or a high level of apomixis in the cultivated species and be able to readily hybridize cross-compatible sexual x apomictic genotypes to produce true-breeding F1 hybrids.
Soybean, Glycine max (L), is a valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding soybean varieties that are agronomically sound. The reasons for this goal are to maximize the amount of grain produced on the land used and to supply food for both animals and humans. To accomplish this goal, the soybean breeder must select and develop soybean plants that have the traits that result in superior varieties. Current known varieties of soybeans show a percent conversion of less than 50% for conversion of flowers to pods and usually about 50 pods per plant.
Therefore it would be desirable to have a variety of soybeans that have a higher percent conversion and a greater number of pods per plant. It would further be desirable if there were a facile method for producing such a variety.